#include <cmath>
#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
#include <map>
#include <set>
#include <cstring>
#define endl "\n"
using namespace std;
int main()
{
	string str;
	int k,ss=0,kk=1;
	cin >> k >> str;
	
	for (int i = 0;i<str.size(); i++)
	{
		if (str[i] != str[i + 1])
		{
			if (kk >= k)
			{
				cout << str[i];
				return 0;
			}
			kk = 1;

		}
		else
			kk++;
	}
	cout << "Ok";
	return 0;
}